"'SpongeBob SquarePants' is about a sponge who lives under the sea in a pineapple," said Banks. "He works at the Krusty Krab, he makes Krabby Patties. ...

"Then there is Plankton, who is the evil little bit of plankton who wants nothing more than to get the secret recipe to get Krabby Patties, which will allow him for some reason to take over the world."

Of course SpongeBob is not a sea sponge but an actual kitchen sponge. He works as a fry cook in a place called Bikini Bottom with what you might call a "colorful" cast of characters and assorted misfits.

"Funny is funny, [and] the actors are all very good," said Roger Bumpass, who voices Squidward. "The stories are funny, it's maintained its longevity."

Bill Fagerbakke plays Patrick. "I think it's SpongeBob's whimsical optimism," he said, "that he cannot be defeated. I think that has a lot to do with its appeal."

Another key to the show's success is that the humor hits for all age groups, said Clancy Brown, who voices Mr. Krabs. "I think adults these days are very immature," Brown said. "We are keeping them immature."

Tom Kenny, the voice of SpongeBob himself, agreed.

"Luckily, the infantilization of the American culture has worked for us," Kenny said.

How a 'SpongeBob' Episode Is Made

The show's creators say they're not necessarily writing kids stuff. A full 25 percent of the show's audience are adults who don't even have kids.

"We are trying to make a show that we would laugh at when we watch," said Banks. "...If you could say 10 million 8-year-olds would love this, every show would be a hit -- and that doesn't happen. So it's what we think is funny."

Making a children's cartoon isn't child's play: It takes nine months to make just one episode.

The artists pitch the shows to executive producer Paul Tibbitt in a room plastered with illustrations, including a storyboard of an episode.

One of their high-tech tools: "Post-It" notes.

"It makes it easy 'cause you can just pull them off and switch 'em around," said Luke Brookshire, a "SpongeBob" artist. "It makes for an easier job of changing things."

A cleaned-up version of the episode is run by a network executive for approval and to make sure nothing offensive slips in.

The deadlines are fierce. It's one of the few cartoons left that still uses paint for animation. So it's not enough to be good or creative--you have to be fast, too.

"That's the ticket here," said Brookshire. "You're on a schedule, so it's kind of creative-on-demand."

The cartoon has been going 10 years now. It's broadcast around the world in 25 languages and it has spawned an entire line of toys, clothing and food, with total sales estimated at nearly $1 billion a year.

Kenny, SpongeBob's voice, said it's good work if you can get it.

"The only reason my family and I aren't living under a bridge is that I can go 'Dahahha!'" Kenny said. "How do you explain that? It's a very bizarre day job!"

Kenny and the rest of the cast practice by rehearsing around a table. When they finally record the show there are no added special effects for their voices.

"Nightline" was given special permission to speak with the Sponge himself -- but only by phone:

Nightline: I'm wondering, where could I get myself some "SquarePants"? Do you mind telling me where you shop?

SpongeBob: Not at all. I'd be happy to tell you. I buy them ... AT THE STORE!!!

Nightline: You seem to be working all the time. Do you ever take a vacation?

SpongeBob: Now that you mention it, it might be nice to go someplace far away where I could just relax and make some Krabby Patties!

Nightline: And finally, my kids really wanted me to ask you this -- what is the Krabby Patty secret formula?